Optical elements are widely used for transmitting optical signals between data exchanging devices and/or communication devices.
Silicon photonics, for example, is rapidly gaining importance as a generic technology platform for a wide range of applications in telecom, datacom, interconnect and sensing. It allows implementing photonic functions through the use of complementary metal-oxide semiconductor (CMOS) compatible wafer-scale technologies on high quality, low cost silicon substrates.
Especially for short distance applications like data communication (datacom), interconnect or access network, the device price may be a major concern. Thanks to silicon mass production, the price of a photonic chip integrating hundreds of basic building blocks can be extremely cheap and economically advantageous. However, the packaging cost can significantly exceed the cost of the single chip so that the final device price can be too high to meet economical market needs or requirements.
The need for efficient fiber coupling may be one of the main reasons for such a high photonics packaging cost. Connecting an optical fiber to a millimeter scale chip may often involve complex alignment procedures with tight mechanical tolerances.
D. W. Vernooy et al., Alignment-Insensitive Coupling for PLC-Based Surface Mount Photonics, IEEE PTL, 2004 describes a way of using adiabatic coupling between III-V chips and silica planar lightwave circuit (PLC). The technology enables surface mount flip-chip of III-V components onto PLC platform with loss <0.5 dB between chips. The III-V chip has a low index contrast output waveguide and the light is transferred from the InP waveguide into this waveguide. (There may be an additional 2 dB on chip loss where the light transitions from III-V to this output waveguide). This allows the mode to expand significantly and can be coupled to a waveguide on the PLC (also low index contrast) provided the surface mount brings them into close enough proximity.
T. Meany, et al., Appl. Phys. A 114 (1), 113-118 (2013) describes using femto-second lasers to write waveguides in glass. This technique is called femto-second laser direct-write (FLDW) and is based on the non-linear absorption of high intensities pulses in a transparent material. As a result, when a laser is focused below the surface of a transparent material, due to a nonlinear effect, the absorption is highly localized at the laser focus point. At low intensities of the laser, a modification of the material's refractive index can be observed, by translating the substrate with respect to the laser focus, it is possible to form a waveguide. This can occur in three dimensions and means that this technique can easily produce low-loss waveguiding at multiple depths.